1. Field of the Invention
The present invention relates to an optical disc device for performing playback operations on optical-disc recording media, and particularly relates to a method for setting the playback power of the optical disc device.
2. Description of Related Art
Compact discs (CDs), digital versatile discs (DVDs), Blu-ray discs (BDs;®), and other optical-disc recording media are currently in widespread use. These optical-disc recording media have one or two recording layers, but multilayer optical-disc recording media having three or more recording layers in order to further expand memory capacity are also being put into use. (In order to differentiate from optical-disc recording media having one or two layers, only optical-disc recording media having three or more recording layers will be referred to as “multilayer optical-disc recording media” below.) For example, in the case of BDs, BDXLs® having three to eight recording layers are being standardized, and BDTLs having three recording layers and BDQLs having four recording layers are being put into use.
For example, Japanese Laid-Open Patent Application No. 2010-186545 discloses a multilayer optical-disc recording medium having seven recording layers capable of recording playback and one recording layer specialized for playback. Japanese Laid-Open Patent Application No. 2010-160864 describes an optical-disc recording medium having n recording layers (where n=2 to 8). Japanese Laid-Open Patent Application No. 2009-140580 describes an optical-disc recording medium having two or three or more recording layers. Japanese Laid-Open Patent Application No. 2003-257072 describes the development of an optical-disc recording medium having a plurality of recording layers.
However, greater optical output is required for multilayer optical-disc recording media having three or more recording layers than for conventional optical-disc recording media having one or two recording layers. Therefore, when the optical-disc recording medium is mounted in an optical disc device, when an optical-disc recording medium having one or two recording layers is erroneously determined to be a multilayer optical-disc recording medium having three or more recording layers, the optical output may be set excessively high. In such instances, the optical-disc recording medium is degraded or destroyed by the optical output (i.e., the playback power) during playback operations.
For example, in BDs, the reflectivity of the recording surface is lower than in CDs, DVDs, and the like, and the protective layer on the recording surface is extremely thin. Even when the mounted optical-disc recording medium is BDSL or BDDL, the medium may be readily mistaken for BDXL due to undulations or warping of the BD, focusing errors, or other issues. When playback operations are performed on the BDSL or BDDL, and the playback power is set for BDXL, the BDSL or BDDL will be degraded or destroyed.
Japanese Laid-Open Patent Application No. 2010-186545 merely discloses that the playback power for the recording layer that allows recording and playback is set when playing back the address information of the optical-disc recording medium. Japanese Laid-Open Patent Application No. 2010-160864 discloses a method for determining the number of recording layers in a multilayer optical-disc recording medium, but a process for cases where the number of recording layers of the multilayer optical-disc recording media is erroneously determined is not described. The aforedescribed problem therefore cannot be resolved. Japanese Laid-Open Patent Application No. 2009-140580 sets the playback power to a standard playback power and then obtains an optimal playback power for the multilayer optical-disc recording medium on the basis of the amount of change in a jitter value measured while changing the playback power by predetermined amounts. However, the only standard playback power described is a low power that is susceptible to the effects of laser noise. Japanese Laid-Open Patent Application No. 2003-257072 merely discloses setting playback power and recording power on the basis of the results of determining whether the optical-disc recording medium has one recording layer or two recording layers.
Thus, even in Japanese Laid-Open Patent Application No. 2010-186545, Japanese Laid-Open Patent Application No. 2010-160864, Japanese Laid-Open Patent Application No. 2009-140580, and Japanese Laid-Open Patent Application No. 2003-257072, when an optical-disc recording medium having one or two recording layers is erroneously determined to be a multilayer optical-disc recording medium having three or more recording layers, the playback power will cause the optical-disc recording medium to be degraded or destroyed.